Production of a thermoplastically processable, aromatic polyamide using a 4-phenoxypyridine stabilizer

ABSTRACT

An aromatic polyamide, e.g., from isophthalic acid and 4,4&#39;-bis(4-aminophenoxy)diphenylsulfone, is produced with a sufficient amount, e.g., 0.05-4 mol%, of 4-phenoxypyridine to improve resistance to thermal oxidation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to copending, coassigned applicationentitled Production of Aromatic Polyamides with High Purity Monomers[Attorney's Docket No. HUELS 732] and copending, coassigned applicationentitled Production of Aromatic Polyamides with Fused Ring Stabilizer[Attorney's Docket No. HUELS 733].

BACKGROUND OF THE INVENTION

The invention relates to a process for the production ofthermoplastically processable, aromatic polyamides, resultantcompositions and articles of manufacture made therefrom.

Conventional polyamides are produced by the polycondensation of thestarting monomers set forth below:

(A) HOOC--Ar--COOH

(B) H₂ N--Ar'--NH₂

with the following meanings:

Ar: 1,3- or 1,4-phenylene; 1,4-,1,5-, 2,6- or 2,7-naphthylene, ##STR1##X: --SO₂ --; --CO--; Y: --O--; --S--;

Z: --O--; --S--; --SO₂ --; --CO--; --CR₂ --; or a single bond;

R: --H; C₁ --C₄ --alkyl;

in the melt in the presence of 0.05-4 mol %, based on the sum total ofcomponents (A) and (B), of a phosphorus-derived acid of the generalformula H₃ PO_(n) wherein n=2 to 4, or triphenyl phosphite, attemperatures in the range of 200° to 400° C.

The production of such polyamides is basically known (DOS 3,609,011).Because the melt viscosity of these aromatic polyamides is high, evenhigher temperatures are required during their manufacture andprocessing, generally at least 350° C. At these temperatures, damage tothe product is frequently observed, recognizable by discolorations or animpairment of the mechanical properties.

SUMMARY OF THE INVENTION

An object of the invention is to provide molding compositions based onaromatic polyamides which do not exhibit the aforedescribeddisadvantages of the prior art products.

Another object is to provide a process for producing the polyamides forsuch compositions.

Still another object is to provide articles of manufacture produced fromsuch molding compositions.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

These objects are attained by performing the polycondensation reactionin the presence of a sufficient amount of 4-phenoxypyridine to stabilizethe resultant polyamides against thermal oxidation, generally 0.05-4 mol% of 4-phenoxypyridine, based on the sum total of components (A) and(B).

Preferably, 4-phenoxypyridine is utilized in amounts of 0.2-2 mol %,based on the total mols of components (A) and (B).

For the production of the aromatic polyamides, suitable aromaticdicarboxylic acids (component A) include but are not limited toisophthalic acid, terephthalic acid, 1,4-, 1,5-, 2,6-,2,7-naphthalenedicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acidor 4,4'-benzo-phenonedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylicacid, 2-phenoxyterephthalic acid or mixtures thereof.

Likewise, suitable aromatic diamines (component B) include but are notlimited to, for example, 4,4'-bis(4-aminophenoxy)diphenylsulfone,4,4'-bis(3-aminophenoxy)-diphenylsulfone,4,4'-bis(4-aminophenoxy)benzophenone,4,4'-bis(3-aminophenoxy)benzophenone,4,4'-bis(p-aminophenylmercapto)diphenylsulfone or mixtures thereof.

The preferred components are (A) isophthalic acid and (B)4,4'-bis(4-aminophenoxy)diphenylsulfone.

The molar ratio in which components (A) and (B) are used ranges at about1:1.

In order to achieve an improvement in the hydrolysis resistance of thepolyamides, it is optional to add to the products of this invention0.01-10 mol %, based on the sum total mols of components (A) and (B), ofa low-molecular aliphatic, araliphatic or aromatic carboxylic acidamide. In this context, the aromatic residue can be substituted byhalogen or by C₁ - to C₄ -alkyl residues. This advantage has beendisclosed in DOS 3,804,401. Preferred aliphatic carboxylic acid amidesare acetic acid N-ethylamide, butyric acid N-ethylamide, butyric acidN-decylamide, or propionic acid N-octylamide; preferred araliphaticcarboxylic acid amides are benzoic acid N-butylamide, toluic acidN-butylamide, and butyric acid N-phenylamide; and preferred aromaticcarboxylic acid amides are benzanilide, 4-chlorobenzoic acid anilide,tolyl-anilide, benzoic acid N-(4,4'-phenoxy)diphenylsulfonamide, and2-naphthalenecarboxylic acid anilide.

It is also possible, moreover, to prepare the low-molecular weightcarboxylic acid amides with the aid of amide-forming compounds in thereaction mixture proper, i.e., in situ. In this case, amide-formingcompounds, such as aromatic monocarboxylic acids, e.g., benzoic acid,naphthalenecarboxylic acid or chlorobenzoic acid, and/or aliphaticmonocarboxylic acids of 1-20 carbon atoms, are made to react witharomatic monoamines, for example, aniline, chloroaniline, naphthylamine,4-(4-aminophenoxy)diphenylsulfone, and/or aliphatic amines of 4-20carbon atoms. The carboxylic acid and amine are preferably used inequimolar amounts.

The glass transition temperatures (T_(g)) of the polyamides according tothis invention are in the range of about 190°-270° C. and the viscositynumbers (J values) are about 30-100 cc/g, preferably 60-80 cc/g. (Jvalues are also known as intrinsic viscosities, limiting viscositynumbers, and the Staudinger index, Rompper 8th edition, Vol. 6, p.4532).

As indicated above, the production of the aromatic polyamides isbasically conventional and described, inter alia, in DOS 3,609,011,i.e., by the polycondensation of components (A) and (B) in the presenceof aphosphorus-derived acid of the general formula H₃ PO_(n) wherein n=2to 4 inclusive, or triphenyl phosphite.

Suitable acids derived from phosphorus are hypophosphorous acid,phosphorous acid, phosphoric acid.

The catalyst is utilized in catalytic quantities, generally in amountsof 0.05-4 mol %, preferably 0.02-2 mol %, based on the sum total ofcomponents (A) and (B). The catalyst and 4-phenoxypyridine arepreferably utilized in equimolar amounts.

The reaction is performed in the melt at temperatures ranging from about200° to 400° C., preferably 230°-360° C., and conventionally carried outunder an inert gas and under normal pressure. However, superatmosphericpressure or a vacuum can likewise be used.

In order to increase molecular weight, the aromatic polyamides can besubjected to solid-phase recondensation in an inert gas atmosphere.

The polyamides can be processed by means of conventional machines intomolding compositions which can also additionally contain fillers, suchas talc, or reinforcing media, such as glass fibers, aramid fibers, orcarbon fibers, as well as other usual additives, such as, for example,pigments and/or stabilizers.

The molding compositions are processed into molded parts, fibers, films,etc., in accordance with conventional methods, such as injectionmolding, extrusion, or similar processes. Use as a coating agent islikewise possible, starting with powder (e.g., fluidized bed coatingmethod), a liquid dispersion, or a solution.

Aromatic polyamides produced in accordance with the process of thisinvention exhibit an unexpectedly high temperature stability. Processingof the products can take place even at temperatures of above 340° C.without the occurrence of a drop in molecular weight or browndiscoloration. Furthermore, molding compositions obtained according tothe invention show excellent stability with respect to thermal oxidationso that they can be utilized even at markedly higher temperatures thancorresponding prior art compositions.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the following examples, all temperatures are setforth uncorrected in degrees Celsius and unless otherwise indicated, allparts and percentages are by weight.

The entire disclosure of all applications, patents and publications,cited above and below, and of corresponding German application P 39 05883.2, are hereby incorporated by reference.

The glass transition point (T_(g)) referred to in this specification wasdetermined with the use of a differential scanning calorimeter (DSC) ata heating rate of 10° C./min.

The viscosity numbers (J) referred to in this specification weredetermined by using 0.5% by weight solutions of the polymers in aphenol/o-dichlorobenzene mixture (1:1 part by weight) at 25° C. inaccordance with DIN 53 728.

Examples identified by letters are not in accordance with thisinvention.

The 4-phenoxypyridine is a well known compound, per se, and is produced,e.g., by reacting 4-chloropyridine with sodium phenolate.

EXAMPLES Example 1

A melt was prepared from 21.62 g (0.05 mol) of4,4'-bis(4-aminophenoxy)diphenylsulfone and 8.31 g (0.05 mol) ofisophthalic acid with 155 mg (0.0005 mol) of triphenyl phosphite and85.5 mg (0.0005 mol) of 4-phenoxypyridine in a polycondensation reactorequipped with agitator, nitrogen inlet and distillation bridge at 250°C. The temperature was raised to 300° C. after 20 minutes. During thisstep, the viscosity of the melt was constantly on an increase while thewater liberated during the course of the reaction was removed bydistillation. After 30 minutes at 300° C., the reaction was stopped.

The viscosity number (J) was 38 cc/g. A solid-phase recondensation at250° C. and 0.5 mbar yielded a polyamide with J=63 cc/g after 24 hours.

Example 2

21.62 g (0.05 mol) of 4,4'-bis(4-aminophenoxy)-diphenylsulfone, 6.64 g(0.04 mol) of isophthalic acid and 1.66 g (0.01 mol) of terephthalicacid were reacted with 81 mg (0.001 mol) of H₃ PO₃ and 171 mg (0.001mol) of 4-phenoxypyridine analogously to Example 1.

The viscosity number was 45 cc/g after 30 minutes at 300° C. Thesolid-phase recondensation conducted analogously to Example 1 yielded apolyamide with J=74 cc/g.

Example 3

21.62 g (0.05 mol) of 4,4'-bis(4-aminophenoxy)-diphenylsulfone and 8.31g (0.05 mol) of isophthalic acid were reacted analogously to Example 1with 109 μl (0.001 mol) of 50% by weight aqueous hypophosphorous acidand 171 mg (0.001 mol) of 4-phenoxypyridine.

The viscosity number (J) was 43 cc/g. The solid-phase recondensationconducted analogously to Example 1 yielded a polyamide with J=75 cc/g.

Example A (DOS 3,609,001)

21.62 g (0.05 mol) of 4,4'-bis(4-aminophenoxy)-diphenylsulfone, 8.31 g(0.05 mol) of isophthalic acid and 109 μl (0.001 mol) of 50% aqueoushypophosphorous acid were reacted analogously to Example 1.

The viscosity number (J) was 32 cc/g. A solid-phase recondensationconducted analogously to Example 1 yielded a polyamide with J=62 cc/g.

Example B (DOS 3,609,011)

21.62 g (0.05 mol) of 4,4'-bis(4-aminophenoxy)-diphenylsulfone and 8.31g (0.05 mol) of isophthalic acid were reacted with 109 μl (0.001 mol) of50% by weight aqueous hypophosphorous acid and 122 mg (0.001 mol) of4-dimethylaminopyridine analogously to Example 1.

The viscosity number (J) of the polyamide was 35 cc/g. After asolid-phase recondensation conducted analogously to Example 1, apolyamide was obtained with J=75 cc/g.

The polyamides produced in Examples 1 to 3, as well as in thecomparative examples were compression-molded into panels having athickness of 1 mm at 310° C. and under a pressure of 100 bar, and storedin a recirculating air oven with a fresh air feed of about 10 vol % for24 hours at 200° C. The polyamides produced in accordance with the stateof the art showed a very strong dark-brown discoloration whereas thepolyamides produced in accordance with this invention exhibited nochange in color.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. A process for producing a thermoplasticallyprocessable, aromatic polyamide by polycondensation of the followingstarting monomers:(A) HOOC--AR--COOH (B) H₂ N--Ar'--NH₂ wherein Ar is1,3- or 1,4-phenylene, 1,4-, 1,5-, 2,6- or 2,7-naphthylene, ##STR2## Xis --SO₂ -- or --CO--; Y is --O-- or --S--; Z is --O--; --S--; --SO₂ --;--CO-- or --CR₂ -- or a single bond; R is --H or C₁ --C₄ --alkyl;in themelt in the presence of 0.05-4 mol %, based on the total mols ofcomponents (A) and (B), of an acid of the formula H₃ PO_(n) wherein n is2 to 4 inclusive, or triphenyl phosphite, at a temperature of about200°-400° C., and performing the polycondensation reaction in thepresence of 0.05-4 mol %, based on the total mols of components (A) and(B), of 4-phenoxypyridine.
 2. A process according to claim 1, whereinthe 4-phenoxypyridine is contained in the reaction mixture in an amountof 0.2-2 mol %, based on the total mols of components (A) and (B).
 3. Aprocess according to claim 1, wherein the 4-phenoxypyridine is containedin the reaction mixture in about equimolar quantities, based on thephosphorus compound.
 4. A composition produced by the process ofclaim
 1. 5. An article of manufacture made by molding a moldingcomposition comprising the composition according to claim
 4. 6. Acomposition produced by the process of claim
 2. 7. A compositionproduced by the process of claim
 3. 8. An article of manufacture made bymolding a molding composition comprising the composition according toclaim
 6. 9. An article of manufacture made by molding a moldingcomposition comprising the composition according to claim
 7. 10. Amelt-polymerized aromatic polyamide produced with a sufficient amount of4-phenoxypyridine in the melt to improve resistance to thermaloxidation.
 11. An article of manufacture made by molding a moldingcomposition comprising the composition according to claim
 10. 12. Amethod of improving resistance to thermal oxidation of amelt-polymerized aromatic polyamide, comprising adding a sufficientamount of 4-phenoxypyridine to the melt to improve resistance to thermaloxidation.